Plasmoid generator and accelerator utilizing an annular magnetic core



May 9, 1967 W. HERTZ 3,3119,W@

PLASMOID GENERATOR AND ACCELERATOR UTILIZING AN ANNULAR MAGNETIC CORE Filed Dec. 18, 1964 3 Sheets-Sheet 1 ay 9, 1967 W. HERTZ 9 9 TOR A NUI AR PLASMOID GENERA ND ACCELERATOR UTILIZING AN AN J MAGNETIC CORE Filed Dec. 18, 1964 3 Sheets-Sheet 2 lHililllllllllilllll-Il W PEG, 4,

May 9, 1967 w. HERTZ 3,319,,Wfi

PLASMOID GENERATOR AND ACCELERATOR UTILIZING AN ANNULAR MAGNETIC CORE Filed Dec. 18, 1964 5 Sheets-Sheet 5 FIG. 8

PLASMUHD GENERA TQEQ AND ACCELERATGR UTELEZENG AN ANNULAR MAGNETIC CGRE Walter Hertz, Erlangen, Germany, assignor to Siemens- Schuclrertwerke Aktiengesellschaft, Berlin-Siemensstadt and Erlangen, Germany, a corporation of Germany Filed Dec. 18, 1964, Set. No. 419,426 Claims priority, application Germany, Dec. 21, 1963,

88 842 is Ciaims. or. 313161) My invention relates to an electrodeless apparatus for generating and accelerating plasmoids.

It has already been suggested in copending application Ser. No. 349,996, now Patent No. 3,270,236, to Alois Koller et al. to produce a magnetic field having a radial component, a so-called cusp field, in a tubular vessel of insulating material between two magnetic field coils arranged in axially spaced relation on the tubular vessel and having mutually opposed windings, i.e. being of mutually opposed magnetic action. An electric field perpendicular to the radial magnetic field is produced according to the aforementioned copending application with a low induction winding or induction coil disposed on the insulating tube. This electrical field is circular and is induced in the interior of the tubular vessel by a varying magnetic field resulting from exciting the coil by a pulsating or periodic electric current. When the tubular vessel contains gas, a plasma is produced therein by the circular electrical field and a ring-flow of electric current is generated in the radial magnetic field of the aforementioned magnetic field coils. The Lorentz force resulting from the circulating fiow of electric current in the plasma and the radial magnetic cusped field of the two field coils exerts an accelerating force upon the plasma having a component in the axial direction of the tubular vessel. It the accelerated plasma were to be shot (extracted) out of one of the known apparatuses, ditficulties would be encountered. The plasma is accelerated over magnetic field lines and surrounds these. At the other end of one of the magnetic field coils of the coil pairs forming the cusp magnetic field, the current conducting plasma is again retarded because there the radial components of the magnetic field have opposing direction to that of the cusp magnetic field. This barrier or obstacle has largely been overcome until now with additional devices such as a second induction coil or guide coil traversed by a current travelling in a direction opposite to that of the first induction coil. These devices, however, require spacious electronic control apparatus and among other things the individual supplemental induction coils must be energized after the first induction coil in time intervals accurately adhered to that are of the order of magnitude of a microsecond.

It is accordingly an object of my invention to provide a plasmoid accelerator which avoids the disadvantages of the known apparatuses of this general type. More particularly, it is an object of my invention to provide a plasmoid accelerator with a single induction coil and a single field coil which will produce a plasmoid that is predominantly field-free.

With these objects in view I provide an electrode-less apparatus for producing and/or accelerating plasmoids over electromagnetic paths in intersecting electrical and magnetic fields within a tubular vessel of insulating material whereby the electrical field extending along the azimuth in the tubular vessel is produced by a pulsating or periodically energized Winding of low induction (induction coil) located on the exterior of the insulating tube. In accordance with another aspect of my invention, the induction coil is inserted in the outer rim of a cup-shaped tates Patent magnetic circuit structure having an inner, central core, the outer rim portion of the structure being formed as an annular pole shoe. The magnetic circuit structure surrounds a closed end of the tubular vessel and a magnetic field coil is located in or on the core thereof extending up to the vicinity of the pole shoe.

In accordance with my invention, the field coil which excites the magnetic circuit can be located in or on the core either inside the tubular vessel or outside the tubular vessel. The field coil can, moreover, be surrounded by a cylinder of electrically conductive material and/or can be inserted inside the core which may be formed as a hollow cylinder.

In accordance with a further aspect of my invention, the field coil that is employed can be a superconductive coil. By means of the surrounding cylinder of conductive material (shielding cylinder), which can consist of brass especially, or by means of the core formed as a hollow cylinder enclosing the field coil, rapidly varying magnetic fields of the induction coil which might disturb the superconductivity are kept away from the field coil.

In accordance with another aspect of my invention, 1 provide a plasmoid accelerator in which the plasmoid which is produced is free of the magnetic field of the field coil and can therefore leave the apparatus with unreduced velocity.

According to an additional aspect of my invention, I provide a plasmoid accelerator in which a magnetic field with a large radial component extending in the plane of the induction coil is produced in the tubular vessel by passing the magnetic flux through ferromagnetic material.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in a plasmoid generator and accelerator, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of the equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIGS. 1 and 2 are schematic views, partly in section and partly broken away, of two embodiments of my invention;

FIG. 3 is a sectional view of FIG. 1 taken along the line III-III in the direction of the arrows;

FIG. 4 is an enlarged sectional view of a modified component of the embodiment shown in FIG. 1; and

FIG. 5 shows a schematic electric circuit associated with the modified embodiment of FIG. 4.

Referring now to the drawings and particularly first .to FIGS. 1 and 3, there is shown a magnetic field coil 1 within a conductive shielding cylinder 2 which forms the hollow core of a cup-shaped magnetic circuit structure 5. The conductive shielding cylinder 2. is mounted coaxially in a tubular vessel 3 of insulating material which consists advantageously of glass or quartz glass and has a diameter of, for example, between 6 and 12 cm. The magnetic flux of the field coil 1 enters the tubular vessel 3 at the location 4. The wall of the cup-shaped magnetic circuit structure is not solid, as clearly seen in FIG. 3, consisting of a spider of bowed, somewhat W-shaped members 5, through which the flux emerging from the other end of the coil is conducted to a plane substantially passing through the location 4. An induction winding or coil 6 is located in this plane on the outside of the tubular vessel 3. The magnetic field lines emerging from the location 4 extend largely in a direction radial to and through the tubular vessel 3 and enter the bow member 5 of magnetic material at the location 7, to close the magnetic circuit.

Whereas the field coil 1 in the embodiment of FIG. 1 is located inside the tubular vessel 3, the embodiment shown in FIG. 2 is provided with field coils and 10a and 11 located outside the tubular vessel 3, and a pole shoe 14 of magnetic material is provided at the core of the magnetic circuit structure 5, the magnetic flux passing through the pole shoe 14 before entering the tubular vessel 3.

By exciting the induction coil 6 with a pulsating electric current, for example having an order of magnitude of 100 kiloamperes for about 0.1 to 10 microseconds duration, the varying magnetic field produced thereby induces a circular electrical field in the tubular vessel 3. A neutral gas under suitable pressure, for example of several Torr, present in the tubular vessel 3, becomes ionized and a ring flow of electric current 9 forms in the plasma as shown in cross section in FIG. 1. The ring of electric current 9 in the plasma acting together with the magnetic field of the field coils exerts an accelerating force (Lorentz force) on the plasma having a component in the axial direction of the tubular vessel 3, the component being represented by the arrow 8 as shown in FIG. 1. By suitably pre-ionizing the plasma-producing gas, for example by high frequency ionization, the formation of the ring current flow 9 can be promoted. With one or more rapidly closeable gas inlet valves 15 of known construction built into the tubular vessel wall (FIG. 5) the plasmoid accelerator can then be used to eject the plasmoids into a non-illustrated vacuum chamber, for example.

FIG. 4 shows a modified coil arrangement for the embodiment of FIG. 1 having a cusp coil 1 which is superconductive and is located in a cryostat. The cryostat consists of cylindrical, coaxial vacuum bottles 24 arranged one within the other and between which there is a space 23 containing liquid nitrogen for example. The outer wall 22 of the cryostat also serves as a shield for the high frequency magnetic fields of the coil 6 (FIG. 1) and is preferably made of brass. The coil 1 in FIG. 4 is completely surrounded by liquid helium contained in the interior chamber 21 of the inner vacuum bottle and does not have a magnetic core if it is to be superconductive. If a normally conducting coil 1 (not superconductive) is employed, such as is described hereinbefore with respect to the embodiment of FIG. 1, for example, a magnetic core of conventional core material can be inserted in the coil 1. The superconductive coil 1 of FIG. 4 has the following characteristics: A field strength of about 5 to 10 kg., 10,000 to 20,000 windings in 6 to 8 layers with niobium-zirconium wire of 0.25 mm. diameter, and the coil 1 and cryostat assembly of FIG. 4 has an over-all diameter of about 40 to 60 mm;

In FIG. 5 there is shown diagrammatically a basic electrical circuit for the embodiment of FIG. 4 where the coil 1 consists of an air core type (if coil 1 were superconductive, a direct current circuit would be used instead of the capacitor discharge circuit shown in FIG. 5). A spark gap 30 and a capacitor 32 are connected by the conductor 38 to the coil 1. The spark gap 30 is ignited by means of a well known igniting device 36. The capacitor 32 can have characteristic values of 40 microfarads and kv. Connected in the return conductor 37 of the coil 1, is an ohmic resistance 34 which has a value between about 0.1 and 1 ohm. The size of the resistance is determined in accordance with the required time constant of the circuitincluding the conductor leads 37 and 38. The leads 37 and 38 are grounded. A Rogowski belt (current transformer) 41 encircles the conductor 37 and provides a current pulse which is conducted to a time delay stage 35 and serves to ignite the spark gap 31. The coil 6 is connected in the conductor 40 as well as a capacitor 33 of 10 microfarads and 20 kv. Return 4. conductor 39 of the coil 6 as well as the conductor 40 are grounded.

I claim:

1. Apparatus for generating and accelerating plasmoids comprising a tubular vessel of electrically insulating material having a closed end, means for supplying a gas, a cup-shaped magnetic circuit structure surrounding the closed end of said tubular vessel, said structure being provided with a magnetic inner central core and having a rim portion forming an annular pole shoe, said core extending into said tubular vessel through said closed end thereof to approximately the plane of said pole shoe, a low-induction winding carried by said pole shoe and coaxially surrounding said tubular vessel, periodic electric energizing means connected to said low-induction winding for periodically producing an electrical field extending in the axial direction of said tubular vessel, and a magnetic field coil carried by the core of said structure and electrically energizable for producing a magnetic field intersecting said electrical field so as to generate plasma from a gas received in said tubular vessel and accelerate the plasma in the axial direction of said tubular vessel.

2. Apparatus for generating and accelerating plasmoids comprising a tubular vessel of electrically insulating material having a closed end, a cup-shaped magnetic circuit structure surrounding the closed end of said tubular vessel, said structure being provided with a magnetic inner central core and having a rim portion forming an annular pole shoe, said core extending into said tubular vessel through said closed end thereof to approximately the plane of said pole shoe, a low-induction winding carried by said pole shoe and coaxially surrounding said tubular vessel, a magnetic field coil carried by the core of said structure, and periodic electric energizing means connected to said low-induction winding and said magnetic field coil for periodically producing respectively an electric field extending in the axial direction of said tubular vessel and a magnetic field extending between said field coil and said pole shoe and intersecting said electric field, so as to generate plasma from a gas received in said tubular vessel and accelerate the plasma in the axial direction of said tubular vessel.

3. Apparatus according to claim 1 wherein said magnetic field coil is mounted on said core on the outside of said tubular vessel.

4. Apparatus according to claim 3 wherein said core includes a pole shoe of magnetic material located inside said tubular vessel.

5. Apparatus according to claim 1 wherein said magnetic field coil is surrounded by a cylinder of conductive material.

6. Apparatus for generating and accelerating plasmoids comprising a tubular vessel of electrically insulating material having a closed end, a cup-shaped magnetic circuit structure surrounding the closed end of said tubular vessel, said structure being provided with a magnetic inner hollow central core and having a rim portion forming an annular pole shoe, said hollow core extending into said tubular vessel through said closed end thereof to approximately the plane of said pole shoe, a low-induction winding carried by said pole shoe and coaxially surrounding said tubular vessel, periodic electric energizing means connected to said low-induction winding for periodically producing an electrical field extending in the axial direction of said tubular vessel, and a magnetic field coil mounted in the hollow core of said structure and electrically energizable periodically for producing a pulsating magnetic field intersecting said pulsating electrical field so as to generate plasma from a gas received in said tubular vessel and accelerate the plasma in the axial direction of said tubular vessel.

7. Apparatus according to claim 1 wherein said magnetic field coil is superconductive.

8. Apparatus according to claim 7 wherein said core comprises a cryostat enclosing said field coil for cooling said field coil to superconductive temperature.

5 6 9. Apparatus according to claim ll including a rapidly References Cited by the Examiner close aole gas inlet valve in a vvall of said tubu1ar vessel FOREIGN PATENTS providing an outlet for plasmoids from said vessel.

10. Apparatus according to claim ll wherein said cup- 449,543 6/1948 Canadashaped magnetic circuit structure is in the form of a spider and comprises a plurality of bowed members joined at 5 JAMES LAWRENCE Primary Examiner said core. S. D. SCHLOSSER, Assistant Examiner. 

1. APPARATUS FOR GENERATING AND ACCELERATING PLASMOIDS COMPRISING A TUBULAR VESSEL OF ELECTRICALLY INSULATING MATERIAL HAVING A CLOSED END, MEANS FOR SUPPLYING A GAS, A CUP-SHAPED MAGNETIC CIRCUIT STRUCTURE SURROUNDING THE CLOSED END OF SAID TUBULAR VESSEL, SAID STRUCTURE BEING PROVIDED WITH A MAGNETIC INNER CENTRAL CORE AND HAVING A RIM PORTION FORMING AN ANNULAR POLE SHOE, SAID CORE EXTENDING INTO SAID TUBULAR VESSEL THROUGH SAID CLOSED END THEREOF TO APPROXIMATELY THE PLANE OF SAID POLE SHOE, A LOW-INDUCTION WINDING CARRIED BY SAID POLE SHOE AND COAXIALLY SURROUNDING SAID TUBULAR VESSEL, PERIODIC ELECTRIC ENERGIZING MEANS CONNECTED TO SAID LOW-INDUCTION WINDING FOR PERIODICALLY PRODUCING AN ELECTRICAL FIELD EXTEND- 